This River Awakens by Steven Erikson

Second Hand 

A time to escape
Twelve-year-old Owen Brand and his family move to Middlecross, a riverside town in rural Canada, hoping to leave poverty and unhappiness behind.

A time for innocence
Owen meets three local boys, and they soon form an inseparable band. Over the summer holidays they create their own world, a place apart from the adults who watch over them. Owen also grows close to Jennifer, a fascinating but deeply troubled girl.

And a time to grow up
Then the gang stumble across a body in the river – a discovery with unimaginable consequences for them and the town, from which there is no going back.